Dielectric liquid for electrical apparatus



Dec. 13, 1938. 1 Q FORD ET AL ,2,139,947

DIELECTRIC LIQUID FOR' ELECTRICAL APPARATUS Dec. 13, 1938. v J. G. FORD ET AL DIELECTRIG LIQUID Foa ELECTRICAL APPARATUS FiledlMarch 30, 1957 4 Sheets-Sheet 2 y phenyl R w o z 4 in zo V INVENTO R5 f'me 'and Y- lop f WITNESSES: W

Dec- 13, 1938. J. G. FORD ET AL 2,139,947

DIELECTRIC LIQUID FOR ELECTRICAL APPARATUS Filed March 5o, 1937 4 sheeysneet a De. 13, 1938. J. G. FORD ET AL 2,139,947

DIELECTRIC LIQUID FOR ELECTRICAL APPARATUS Filed `March 3o, 195'? 4 sheets-sheet 4 1% f /1/ a" /2 a N00. rcen of Hexac or 1p ny Empemure "Ehren/:eff Onde [son-)era WITNESSES: INVENTORS Patented Dec. 13, 1938 UNITED STATES DIELECTRIC LIQUID FOR ELECTRICAL AP- PARA TUS

James G. Ford, Forest Hills, and Charles F. Hill,

Edgewood, Pa.,

assignors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 30, 1937, Serial No. 133,924

32 Claims.

The invention relates to dielectric liquids for electrical apparatus and the insulating of the electrical apparatus, and this application is a continuation-in-part of applications Serial Nos.

53,096 and 53,097,

The object of the invention is to provide a .dielectric liquid for electrical apparatus which is chemically stable under ordinary operating conditions, reproof and which when decomposed, produces incornhustible gases.

It is also an object of the invention to provide a dielectric liquid for electrical apparatus which undergoes little physical change through the range of temperatures to which electrical apparatus is normally subjected, thereby enabling its use under all working conditions for such apparatus.

A further object .of the invention is to provide for insulating electrical apparatus with a dielectric which on decomposition by a electric arc,

generates substantially incombustible gases.

For a fuller understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in

which:

Figure 1 is a graph showing how the freezing point of the base liquid varies as the percentages of ethyl-tetrachlorbenzene isomers and ethyl- $0 pentachlorbenzene are varied; l

Fig. 2 is a graph showing how the viscosity of mixtures of the dielectric liquid varies with changes in temperature;

Fig. 3 is a graph showing the effect on freezing point and viscosity of the addition of a freezing lpoint depressor to a mixture of 50% by weight ethyl-tetrachlorbenzene isomers and ethyl-pentachlorbenzene and 50% by weight of an iscmeric pentachlordiphenyloxide mixture;

Fig. 4 is a graph showing the effect of introducing freezing point depressors to a mixture of ethyl-tetrachlorbenzene isomers, ethyl-pentachlorbenzene and chlorinated diphenyloxide; Y

Fig. 5 is a graph showing how the freezing point of the dielectric liquid changes as the percentages of the ingredients are varied; l

Fig. 6 is a view partly in side elevation and partly in section showing the manner in which the coils and core of a transformer are immersed in the dielectric liquid;

Fig. 7 is a view in side elevation of a capacitor built in accordance with this invention and having parts broken away showing details of the construction;

Fig. 8 is a view in side elevation of a sectionof cable constructed in accordance with this invention and having parts broken away to show details of ther structure;

Fig. 9 is a graph showing the specific inductive capacity and percentage power factor for cycle current plotted on temperature in both degrees centigrade and degrees Fahrenheit, for different dielectric mixtures, such as may be employed in the construction of the electrical apparatus in accordance with the teaching of this inv'ention; and

Fig. 10 is a graph showing the 60-cycle resonance temperature of mixtures of ethyl-tetrachlorbenzene isomers, ethyl-pentachlorbenzenes and hexachlordiphenyloxide isomers.

In preparing our dielectric liquid, we employ a base mixture comprising ethyl-tetrachlorbenzene isomers and ethyl-pentachlorbenzene. This mixture may be prepared in a number of ways. For example, by the Friedal-Crafts synthesis, which comprises treating ethylchloride with benzene in the presence of an aluminum chloride catalyzer. The ethylbenzene produced is then chlorinated by bubbling chlorine through it.

Referring to Fig. 1, it will be noted that as the relative proportion of the isomers of ethyl-tetrachlorbenzene to ethyl-pentachlorbenzene is increased in our base liquid, the freezing .point of the mixture decreases. This gives us considerable flexibility in preparing our dielectric from this base material. For instance, if a very low freezing point is required, we may use a base liquid rich in ethyl-tetrachlorbenzene isomers or we may use a base liquid rich in ethyl-pentachlorbenzene and obtain the desired freezing point by the addition of a freezing point` depressor to the mixture. The composition of the final liquid would be determined by the other characteristics desired together with production costs.

Ethyl-tetrachlorbenzene isomers and ethylpentachlorbenzene both have excellent electrical properties, and it follows that mixtures of the two also have good electrical properties. However, ethyl-pentachlorbenzene has a slightly better power factor ,than the isomeric mixture of fthe ethyl-tetrachlorbenzene and in some in. stances, the higher percentages of ethyl-pentachlorbenzene in the base liquid are preferred. 'Referring to Fig. l, it Vwill be noted that the ethyl-pentachlorbenzene freezes at about 125 F. and the isomeric mixture of the ethyl-tetrachlorbenzenes freezes at about F., also that the different mixtures of these materials give intermediate freezing points.

In the interest of manufacturing conomylof the liquid dielectric, the base liquid containing 4080% ethyl-pentachlorbenzc-ne is generally preferred, particularly since the material can generally be handled as a liquid for blending purposes. With the higher percentages of ethylpentachlorbenzene present, crystallization of the super-cooled liquid will sometimes take place on standing at ordinary temperature. For this reason, it is oftentimes advantageous to use the base liquid with lower percentages of ethyl-pentachlorbenzene.

In order to lower the freezing point of our base liquid, chlorinated diphenyloxide isomers are employed. This latter compound has good electrical characteristics and when mixed with the base liquid containing 30% ethyl-tetrachlorbenzene isomers and 70% ethyl-pentachlorbenzene in a 70-30 ratio lowers the freezing point from about 100 F. to about 25 F. The boiling point of such a mixture is about 560 F. Therefore, it has a liquid range of 25 F. to +560 F. and Acan be used efliciently throughout the ranges of temperatures normally encountered in practice.

The amount of chlorinated diphenyloxide isomers employed with the base liquid may be varied through a wide range. Good results have been obtained by employing from 20% by weight to by weight chlorinated diphenyloxide isomers with the base liquid. For most purposes, from about 30% by weight to 70% by weight chlorinated diphenyloxide isomers will be employed with from 70% by weight to 30% by weight of the base liquid comprising ethyl-tetrachlorbenzene isomers and ethylpentachlorbenzene in the ratio of about 30:70. a

A number of specific mixtures of the dielectric which have been found to be satisfactory are as follows:

Per cent by weight Ethyl-tetrachlorbenzene isomers 21 Ethyl-pentachlorbenzene -I 49 Hexachlordiphenyloxide isomers 30 This dielectric mixture has a freezing point of 20 F., a flash point of 355 F., boils at 590 F., and willnot The power factor for 60- cycle current and at room temperature is .05%.

Per cent by weight Ethyl-tetrachlorbenzene isomers 9 Ethyl-pentachlorbenzene 21 Pentachlordiphenyloxide isomers 70 The freezing point of .this dielectric mixture is about 20 F. It has a boiling point of 610 F., and a flash point of 370 F., and it will not burn. The power factor for 60-cycle current at room temperature is also about .05%.

Per cent' by weight Ethyl-tetrachlorbenzene isomers 49 Ethyl-pentachlorbenzene 21 Pentachlordiphenyloxide isomers 30 Per cent by weight Ethyl-tetrachlorbenzene isomers 50 Hexachlordiphenyloxide isomers 50 'I'his dielectric liquid has a freezing point of about 15 F., a flash point of 315 F., boils at 540 F., and will not burn. The power factor for 60-cycle current at room temperature is about 0.1%.

For many purposes, it may be desirable to provide dielectric liquids with .a freezing point lower than that which may be obtained by employing the above mixtures of ethyl-tetrachlorbenzene, ethyl-pentachlorbenzene and chlorinated diphenyl. In such cases, liquids which are classed freezing point depressors are added.

Good results have been obtained by adding to the dielectric liquids described hereinbefore 10% to 5% by weight of one or more of aryl-trichlortetmlin and the chlorinated alkyl derivatives of benzene in which the alkyl side-chain is saturated, or 5% to 40% by weight trichlorbenzene. The chlorinated alkyl derivatives of benzene that have been found to be satisfactory are isopropyltrichlorbenzene, amyl-pentachlorbenzene, amyltrichlorbenzene isomers, amyl-tetrachlorbenzene isomers, tertiarybutyl-chlorbenzenes (for example, butyl-trichlorbenzene isomers, butyl-tetrachlorbenzene isomers and butyl-pentachlorbenzene), isopropyl-pentachlorbenzene, isopropyltetrachlorbenzene isomers, ethyl-trichlorbenzene isomers and trlchlortoluene isomers.

In using the chlorinated alkyl derivatives of benzene where the chlorine is attached to the' carbon in the ring, there should not be more 'than six or seven carbon atoms in the sidechain. If this limit of carbon atoms in the side chain is exceeded, the quantity of the chlorinated alkyl derivatives of benzene added as a freezing point depressor will have to be reduced to compensate for the number of carbon atoms in order to assure the'obtalning of a substantially incombustible gas if the dielectric is decomposed by an electric arc. It has been found preferable to work with chlorinated alkyl derivatives of benzene hav ing fewer than six or seven carbon atoms in the side-chain because'then it is not necessary to watch with as great care the quantity of the derivatives added.

In this connection, 'it is preferable to employ ethyl-trichlorbenzene isomers or trichlortoluene isomers since they have a smaller number of carbon. atoms in the side-chain. As is well known, ethyl-trichlorbenzene has only two carbon atoms in the side-chain and trichlortoluene has only one. Therefore, these chlorinated derivatives of benzene are highly suitable for use as freezing point depressors.

For some purposes it has been found that trichlorbenzene is not as satisfactory as the other.

freezing point depressors. Trichlorbenzene is not as. stable as some of the other depressors, it increases the power factor more rapidly when used in quantities and will decompose when exposed to light. 'Ihe chief advantage of this liquid as a freezing point depressor is that a dielectric containing considerable quantities of it may be produced at a lower price than when any of the other depressors are employed. It has been found thatfromA 5% to 40% byv weight may be employed. However, it is to be noted that when more than 30% by weight of trichlorbenzene is employed,

the power' factor increases rapidly, and that when as much as 40% by weight is utilized in the interest of reduction in cost, there is some danger of crystallization at sub-normal temperatures. When crystallization occurs, the cooling eect is lost because of poor circulation.

In employingl the freezing point depressors other than trichlorbenzene, good results have been obtained with from 10% to 25% by weight of any one of them, or mixtures of two or more. The particular freezing point depressor or mixtures of them selected will depend on the conditions to be met.

A number of specific mixtures of the dielectric liquid carrying freezing point depressors are as follows:

Per cent by weight Ethyl-tetrachlorbenzene isomers 16.2 Ethyl-pentachlorbenzene 37.8 Pentachlordiphenyloxide isomers 36 Trichlortoluene isomers 10 This dielectric mixture has a. freezing point of 20 F., and boils at 580 F. Tests revealthat it has no true flash point, and that it will not burn even at boiling temperatures. The power factor is low, being about 0.4% for 60-cycle current at room temperature.

Per cent by weight EthyL-ttrachlorbenzene isomers 13.5 Ethylfpentachlorbenzene 31.5 Pentachlordiphenyloxlde or hexachlordiphenyloxide isomers 45 Isopropyl-trichlorbenzene isomers 10 This dielectric gives a freezing point of from 15 to 20 F. A iiash point may occur anywhere from 335 to 345 F. It boils around 590 to; 600 F., and will not burn at the boiling point. The power factor for (iO-cycle current at room temperature is about 0.2%. l

Per cent by weight Ethyl-tetrachlorbenzene isomers 8 l Ethyl-pentachlorbenezene 18.9

Pentachlordiphenyloxide or hexachlordiphenyloxide isomers 63 llirichlortoluene isomers 10 This dielectric. gives a freezing point of from to +10 F. It boils at 600 to 610 F., has

no true ash point, and will not burn at the boiling point. The power factor for 60-cycle current and at room temperature is about 0.4%.

- Per cent by weight Ethyl-tetrachlorbenzene isomers 18.9 Ethyl-pentachlorbenzene 44.1 Pentachlordiphenyloxide isomers 27 Trichlorbenzene isomers l0 This dielectric has a low freezing point which is around 40 F- It boils at 540 F., has a flash point of 320 F., and will not burn at the boiling temperature. The power factor for 60-cycle current at room temperature is 0.4%.

Per cent by weight Pentachlordiphenyloxide or hexachlordiphenyloxide isomers 24.3 Ethyl-tetrachlorbenzene isomers 17 Ethybpentachlorbenzene 39.7 Isopropyl-trichlorbenzene isomers 9 Aryl-trichlortetralin isomers 10 The freezing point of this dielectric mixture is from 20 to 30 F. A flash point occurs at about 310 to 320 F., and it boils at about 560 to 570 F., and will not burn at the boiling temperature. The power factor. is about the same as for the previous mixture, being about.

0.4% for (S0-cycle current at room temperature.

In the chlorination of diphenyloxide isomers, best results will be obtained by introducing from 45% to 65% chlorine by weight. Chlorinated diphenyloxide is also available to the trade at prices which will enable its wide use. Penta- `desirable.characteristics as a depressor.

Boiling range, 270 C. to 328 C.

Fire'point, 230 C.

Flash point, around 160 C.

Specific gravity, 1.35 at 40 C.

Chlorine content, 45% by weight to 58% by weight.

In utilizing chlorinated isopropylbenzenes, it has been found that suitable isopropyl-pentachlorbenzene should have a boiling range of 308 C. to 310 C., melting point of about 45 C., ash point over 200 C., no fire point,'specific gravity 1.43 at 96C., chlorine content 60.5%.

Isopropyl-tetrachlorbenzene isomers are also suitable. In selecting the isomers they should have theA following characteristics Boiling range, 270 C. to 290 C.

Melting point, 10 C.

.Flash point, 180 C..

No fire point. Specific gravity, 1.35 at 96C. Chlorine content, 55%.

Mixtures of isopropyl-tetrachlorbenzene isomers and isopropyl-pentachlorbenzene have very These rlnixtures should have the following characteris- 1cs: A

Boiling range, 270 C. to 310 C. Melting point, 45 C. Flash point, over 200 C. No fire point. Y Specific gravity, 1.37 at 96 C. Chlorine content, 57.2%.

Isopropyl-trichlorbenzene isomers employed as a depressor should have the following characteristics:

Boiling range, 250 C. to 253 C. Melting point, below 40 C. Flash point, 116 C.

`Fire point, 140 C.

Specific gravity, 1.3 at 30C. Chlorine content, about 48%.

Another freezing point depressor that has been used with success is amyl-pentachlorbenzene'.

In using this material it should have the following characteristics:

Boiling range, 165x C. to 185 C. at 10 millimeters pressure.

Melting point, below 0 C. Flash point, 190 C. Fire point, over 200 C.l Speciiic gravity, 1.4 at 20 C.

`Arnyl-trichlorlzienzene and amylfetrachlorbenzene isomers make a suitable mixture. In select` ing mixtures of these materials, the following characteristics should be observed:

Boiling range, 270 C. to 298 C. Melting point, below 0 C. Flash point, about 130 C.

Fire point, 168 C.

Speciflc gravity, 1.252 at 24 C. Chlorine content, about 42.2%.

Ethyl-trichlorbenzene isomers have been found suitable when they have the following characteristics:

Boiling range, 240 C. to 250 C. Melting point, below 40 C.

-Flash point, 123 C.A

Fire point, 149 C. Density, 1.34 at C. Chlorine content, about 51%.

Toluene derivatives have been found suitable as freezing point depressors, trichlortoluene isomers having been found the more satisfactory. In selecting the isomeric mixtures the following characteristics are desirable:

Boiling range, 225 C. to 250 C. Melting point, C.

No flash point.

Specific gravity, 1.572 at 30 C. Chlorine content, about 54.6%.

Tetrachlortoluene isomers and pentachlortoluene have also been found to be useful as freezing point depressors.

It will be obvious to those experienced in the art that in using many of the hereinbefore iden- ,tified freezing point depressors, particularly those that may be classed the lower chlorinated derivatives of isopropylbennes, butylbenzenes and amylbenzenes, care must be taken in blending with the base materials such as mixtures of ethyltetrachlorbenzene and ethyl-pentachlorbenzene, or of these materials mixed with chlorinated diphenyloxide, to obtain a fire-proof dielectric. In other words, the chlorine content of the final dielectric mixture should be or over and the constituents should be so selected that the partial pressures shall be such that the vapors given off on heating will not support combustion or be substantially incombustible.

Tests made on our preferred dielectric liquid reveal that it is non-inflammable and when decomposed electrically evolves incombustible gases. It will not be attempted to explain why all the ingredients individually give off substantially incombustible gases when decomposed, since .they do not all follow the same rule. It will be observed that in the formula for ethyl-tetrachlorbenzene, hydrogen is present in excess of the chlorine. Nevertheless, when decomposed electrically, the gases given off are substantially incombustible. The dielectric liquid, comprising ethyl-tetrachlorbenzene, ethyl-pentachlorbenzene, chlorinated diphenyloxide and one or more of the freezing point depressors, is non-inflammable and the gases given oif on electric decomposition incombustible.

Referring to Fig. 6 of the drawings, a transformer casing or tank Ill is shown with a core II carrying coils I2, all arranged in accordance with standard practice. 'I'he coils I2 are provided with terminal conductors I3. As illustrated, the casing contains a sufficient amount of the dielectric liquid I 4 to completely immerse the coils I2.

In transformers, the dielectric liquid is used primarily for maintaining the proper temperature and insulation. In the interest of economy in the dielectric liquid, only a small amount will be employed, and in order for it to effect the proper heat transfer, provision will be made for circulating it through cooling coils in a manner well known in the art, since it has been employed for years in the oil cooling of transformers. When a dielectric liquid of this kind is employed, and a disturbance occurs in the electrical system resulting in arcing of the transformer, there is no fire hazard since the dielectric liquid will not be burned, and the gases which are given off are incombustible and will smother the arc.

With the advent of non-inflammable dielectric liquids, which when decomposed give otI incombustible gases, the trade demanded that capacitors, cables and other similar electrical apparatus be made fire-proof. This involves the fire-proofing of the insulating materials employed in building such apparatus.

In the construction of capacitors, the plates Il made of some suitable conducting material, such as aluminum foil and the like. are separated by sheets II of insulation or dielectric material. Paper is the material most generally used as a dielectric or insulation between the plates.

In the present invention, the capacitors are re-proofed by treating the paper with a dielectric liquid which" is non-inflammable and which, when decomposed, gives oif a substantially incombustible gas. The problem of fire-proofing cables and other similar electrical apparatus is substantially the same as that of fire-proofing capacitors.

Referringfto Fig. 8, in the manufacture of cables a conductor 2l has applied thereto some suitable insulating material II, such as' a paper wrapping. A lead sheath 22 may be applied for protecting the insulation. Other wrappings may be applied to the cable in accordance with general practice, and will not be described herein since such practice is well known to the art.

If the paper insulation employed in cables which is the equivalent of the paper dielectric in capacitors, is not nre-proofed and an arc is caused by some disturbance in the electrical system in which the cable may be connected, a portion of the cable is likely to be destroyed causing an interruption in operation.

In the present invention, the paper insulation or dielectric employed in both capacitors and will vary with the conditions to which the electrical apparatus may be subjected.

The ratio of ethyl-tetrachlorbenzene and ethylpentachlorbenzene may be varied widely. The per( ntages of each will depend on the application to be made. Mixtures comprising from 20% to 80% by weight ethyl-pentachlorbenzene and 80% to 20% by weight ethyl-tetrachlorbenzene isomers have been found satisfactory because of their good electrical4 characteristics, either alone or as a mixture.

When the chlorinated diphenyloxide is added to a preferred base dielectric liquid comprising about 30% by weight ethyl-tetrachlorbenzene isomers and about '10% by weight ethyl-pentachlorbenzene, the freezing point oi.' the dielectric liquid is lowered to a temperature well below that of either alone. Further, since all the ingredlents have good electrical characteristics, the 7s penetrate the insulating material under vacuum.

In the case of capacitors, when the insulation or paper disposed between the plates has vbeen sufciently treated, the capacitor case I3 is sealed. This impregnating process is well known in the art and will not be described in greater detail.

The desirable characteristics of our dielectric in capacitors may best be understood by reference to. Fig. 9, which gives the power factor of the dielectric employed at different temperatures for different percentages of the ingredients. When a capacitor is treated with a dielectric liquid comprising about 40% by weight of the base liquid comprising ethyl-tetrachlorbenzene and ethyl-pentachlorbenzene in the ratio 30 to 70, and about 60% by weight of an isomeric mixture of hexachlordiphenyloxide compounds, the highest power factor value is reached when the temperature falls to about 15 F. An isomeric mixture of hexachlordiphenyloxide is employed because of its low power factor and nre resisting characteristics.

investigation of the dielectric liquid reveals that an increase in the amount of ethyl-tetrachlorbenzene isomers and ethyl-pentachlorbenzene in the ratio of 30 to 70 respectively, with chlorinated diphenyloxide isomers lowers the temperature at which a change in the specific inductive capacity of any appreciable amount occurs. This is generally described in engineering terms as lowering the resonance point or ternperature. It has also been found that the substitution of pentachlordiphenyloxide for hexachlord-iphenyloxide further lowers the resonance point of the capacitor.

As is well known, the specific inductive capacity of the capacitor does not begin to fall oif appreci-` ably until the power factor rises to its peak. Therefore, the capacity of a capacitor impreghated with 40% by weight of a base liquid comprising 30% by weight ethyl-tetrachlorbenzene isomers and 70% by weight ethyl-pentachlorbenzene and 60% by weight of an isomeric mixture of hexachlordiphenyloxide, does not begin to decrease until the temperature falls to about 15 F. This is of considerable value in many applications of such apparatus. When capacitors impregnated with our dielectric are connected into electrical systems which are exposed to atmospheric temperatures, the system is not thrown out of resonance with ordinary temperatures, but will continue to function at full rated capacity until the temperature falls to about 15 F. Such temperatures are seldom imposed on capacitors.

` Capacitors manufactured in accordance with the teachings of this invention may be utilized to advantage in many different kinds of electrical systems. Since the specific inductive capacity of our present capacitor does not begin to decrease until it reaches the temperature of about 15 F., it may be used to advantage in such electrical and from 80% to 20% by weight chlorinated systems as railway signalling systems. In such an application, ordinary winter temperatures will not change substantially the capacity of the .capacitors and the resonance of .thel signalling circuits will be maintained even if the temperature drops close to 15 F.

Referring to Fig. 5, the curve 23 which was plotted from test results obtained on a dielectric mixture containing about 40% by weight ethyltetrachlorbenzene isomers and ethyl-pentachlorbenzene in the ratio 30 to '70, and about 60% by weight of chlorinated diphenyloxide, reveals that the power factor of the dielectric liquid for 60- cycle current is approximately .02% for a temperature range of from 100 to 0 F. The specific inductive capacity continually increases from about 200 F. to approximately 15 F. The change of the specific inductive capacity in this range oi temperatures is very small, varying from about 4.2 to 5.6. The capacity of the capacitors at 'the different temperatures varies directly with the specific inductive capacity. Therefore, under this wide range of temperatures from 200 F. to 15 F., the capacity of the condenser varies very little and it will -`not throw an electric circuit in which it may be connected, out of resonance and cause it to fail.

By reference to Figs. 5 and 10, it will be seen that a definite relation exists between freezing point and resonance temperatures. These curves show that by proper selection of the percentages of the ingredients of our dielectric liquid a capacitor having a resonance temperature as low as 55 F. may -be produced. For example, a mixture comprising 9% by weight `ethyl-tetrachlorbenzene isomers, 21% by weightethyl-pentachlorbenzene and r70% by weight pentachlordiphenyloxide isomers has an apparent freezing point of 25 F. and a resonance point of about 55 F.

Referring to Fig. 1, it will be observed that as the proportion of ethyl-tetrachlorbenzene isomers is increased in the base mixture of ethyl-tetrachlorbenzene isomers and ethyl-pentachlorbenzene, the freezing point is decreased. Therefore, by changing the composition of our base liquid it is possible to alter the freezing and resonance points of resulting mixtures to suit the application to be made. This givesI considerable flexibility in making our dielectric and, if necessary, mixtures can be made which will have resonance temperatures as low as F. However, in the interest of manufacturing economy and low power factor of resulting capacitors, a. base liquid. comprising 20% to 50% by weight ethyl-tetrachlorbenzene isomers is preferred.

In the case of cables, changes in the specific inductive capacity are not of any great imporand prevents the occurrence of fires or the like when the cable is employed in buildings, tunnels,

and basements. The dielectric liquid employed may be varied within considerable ranges. It has been found that dielectric liquids comprising from 20% to 80% by weight ethyl-tetrachlorbenzene and ethyl-pentachlorbenzene mixed in the ratio of from about 30 to '70 with '70 to 30, respectively,

diphenyloxide, give good results in both capacitors and cables.

A number of specific examples of the dielectric liquid that may be employed in the manufacture of capacitors and cables and other similar electrical apparatus are as follows:

Per cent by weight Ethyl-tetrachlorbenzene isomers 21 Ethyl-pentachlorbenzene 49 Hexachlordiphenyloxide isomers 30 This dielectric liquid has a freezing point of 25 F., a flash point of 355 F., boils at 590 F., but will not burn. The power factor for 6.0-cycle current at room temperature is about .03% and the resonance temperature F. It will, therefore, be evident that a capacitor impregnated with this dielectric liquid may be utilized successfully in electrical systems exposed to very low temperatures.

Per cent by weight Ethyl-tetrachlorbenzene isomers l5 Ethyl-pentachlorbenzene- 35 Pentachlordiphenyloxide isomers or hexachlordiphenyloxide isomers 50 exposed to low temperatures. Per cent by weight Ethyl-tetrachlorbenzene isomers 18 Ethy1-pentachlorbenzene 42 Pentachlordiphenyloxide isomers or hexachlordiphenyloxide isomers 40 The freezing point of this dielectric liquid ranges from 10 to 15 F., and has a flash point of 355 F., boils at 600 to 610 F., but will not burn. The power factor for (iO-cycle current at room temperature is .03% and the resonance temperature is from 40 to 45 F.

Per cent by Weight Ethyl-tetrachlorbenzene isomers 8 Ethyl-pentachlorbenzene 32 Pentachlordiphenyloxide isomers or hexachlordiphenyloxide isomers 60 The freezing point of this dielectric mixture is somewhat higher than the previous specific mixtures given, but it may be used successfully at temperatures ranging from 20 to 30 F., which is its resonance temperature. It freezes at from 5 to 15 F., has a flash point at 360 F., boils at 615 to 620 F., but will not burn. The power factor for -cycle current at room temperature is .02%. i Per cent by weight Ethyl-tetrachlorbenzene isomers 35 Ethyl-pentachlorbenzene 15 Pentachlordiphenyloxide isomers or hexachlordiphenyloxide, isomers 50 The freezing point of this mixture ranges from 10 to 15 F. It boils at about 545 F., has a flash point between 310 and 315 F., but will not burn. 'I'he power factor for 60-cycle current at room temperature is about .07%, which is a little higher than that of the other trichlortetralin,

specific mixtures. I'he resonance temperature is quite low, ranging from about 50 to 60 F.

Per cent by weight Ethyl-tetrachlorbenzene isomers 50 Pentachlordiphenyloxide isomers or hexachlordiphenyloxideA isomers 50 This dielectric liquid will stand very low temperatures. Its freezing point ranges from about 20 to 25 F., and has a resonance temperature of 60 to 70 F. The boiling point is around 540 to 545 F. The flash point of the dielectric is around 310 to 315 F., but it has no fire point. The power factor for 60-cycle current at room temperature is about .1%.

When the term substantially incombustible is used in this application, we mean that when our dielectric liquid is employed in electrical apparatus and is decomposed electrically by an arc and the gases of decomposition mixed with air, generally, they will not burn but if they are ignited at a point of high temperature, flame propagation will be very slow and will not result in detonation because the major volume of the gas will not support combustion.

In this specification, the term aryl-trichlortetralin is employed to designate that three chlorine atoms are bonded to the carbon atoms in the ring structure.

Since certain changes may be made in the above construction and dierent embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. A dielectric liquid for electrical apparatus comprising ethyl-tetrachlorbenzene, ethyl-pentachlorbenzene and chlorinated diphenyloxide.

2. A dielectric liquid for electrical apparatus comprising ethyl-tetrachlorbenzene, chlorinated diphenyloxide and 10% to 25% by weight of a. soluble organic dielectric material for lowering the freezing point of the dielectric liquid.

3. A dielectric liquid for electrical apparatus comprising ethyl-tetrachlorbenzene, ethyl-pentachlorbenzene, chlorinated diphenyloxide and as a freezing point depressor isopropyl--trichlorbenzene.

4. A dielectric liquid for electrical apparatus comprising ethyl-tetrachlorbenzene, ethyl-pentachlorbenzene, chlorinated diphenyloxide and a mixture of isopropyl-trichlorbenzene and arylthe isopropyl-trichlorbenzene and aryl-trichlortetralin being lemployed to lower the freezing point of the dielectric liquid.

5. A dielectric liquid for electrical apparatus comprising from 20% to 80% by weight ethyltetrachlorbenzene and etl'i'yl-pentachlorbenzene and from 80% to 20% by weight chlorinated diphenyloxide.

6. A dielectric liquid for electrical apparatus consisting of from 20% to 80% by weight ethyltetrachlorbenzene and ethyl-pentachlorbenzene, from 80% to 20% by weight chlorinated diphenyloxide,` and as a freezing point depressor isopropyl-trichlorbenzene in amounts varying from 10% to 25% by weight.

7. A dielectric liquid for electrical apparatus consisting of from 20% to 80% by weight ethyltetrachlorbenzene and ethyl-pentachlorbenzene', from 80% to 20% by weight chlorinateddiphenyl.

oxide, and as a freezing point depressor trichlortetralin varying from 10% to 25% by weight.

V8. A dielectric liquid for electrical apparatus comprising from 40% to 60% by weight ethyltetrachlorbcnzene and ethyl-pentachlorbenzene, the ethyl-tetrachlorbenzene and ethyl-pentachlorbenzene being in the ratio of 20 to 80, and 60% to 40% by weight chlorinated diphenyloxide.

9. A liquid dielectric comprising, in combination, 40% to 60% by weight ethyl-tetrachlorbenzene and ethyl-pentachlorbenzene, the ethyltetrachlorbenzene and ethyl-pentachlorbenzene being in the ratio of 20 to 80, 40% toV 60% by weight chlorinated diphenyloxide, and isopropyltrichlorbenzene in amounts from 10% to 25% by weight.

10. A dielectric-liquid for electrical apparatus comprising ethyl-tetrachlorbenzene and chlorinated diphenyloxide.

l1. A dielectric liquid forelectrical apparatus comprising ethyl-pentachlorbenzene and chlorinated diphenyloxide.

12. A dielectric liquid for electrical apparatus comprising ethyl-pentachlorbenzene, chlorinated diphenyloxide and 10% to 25% by weight of a soluble organic dielectric material for lowering the freezing point.

13. A dielectric liquid for electrical apparatus comprising 40% to 60% by weight ethyl-tetrachlorbenzene and ethyl-pentachlorbenzene being in the ratio of to 20 and 60% to 40% by weight of chlorinated diphenyloxide.

14. The method of protecting electrical apparatus provided with an electrical conductor and a casing which comprises interposing between the conductor and casing a dielectric liquid which comprises ethyl-tetrachlorbenzene, ethylpentachlorbenzene and chlorinated diphenyloxide which materials when decomposed by an electric arc generate substantially incombustible gases.

15. The method of protecting electrical apparatus provided with a conductor and casing which comprises interposing between the conductor and casing a dielectric liquidcomprising ethyltetrachlorbenzene,ethyl-pentachlorbenzene,chlorinated diphenyloxide, and at least one of the freezing point depressors of the group consisting of trichlortoluene, trichlorbenzene, isopropyltrichlorbenzene and aryltrichlortetralin, the dielectric materials when decomposed electrically generating substantially incombustible gases.

16. A dielectric liquid for electrical apparatus comprising ethyl-tetrachlorbenzene, ethyl-pentachlorbenzene, chlorinated diphenyloxide and at least one of the freezing point depressors of the group consisting of isopro-pyl-trichlorbenzene, aryltrichlortetralin, trichlortoluene and trichlorbenzene.

1'7. The method of protecting electrical apparatus provided with a conductor and casing which comprises interposing between the conductor and casing a dielectric liquid comprising 30% to 60% by weight of a mixture of ethyltetrachlorbenzene and ethyl-pentachlorbenzene, the mixture consisting of from 20% to 80% by weight ethyl-tetrachlorbenzene and 80% to 20% by weight ethyl-pentachlorbenzene, 60% to 25% by weight chlorinated diphenyloxide and at least one of the freezing point depressors of the group consisting of isopropyl-trichlorbenzene and aryltrichlortetralin, trichlortoluene and trichlorbenzene.

18. A dielectric liquid for electrical apparatus comprising 30% to 60% by weight of a mixture oi ethyl-tetrachlorbcnzene and ethyl-pentachlorbenzene, said mixture comprising 20% to 80% by weight ethyl-tetrachlorbenzene and 80% to 20% by weight ethyl-pentachlorbenzene, 60% to 25% by weight chlorinated diphenyloxide and the remainder trichlorbenzene for lowering the freezing point, the dielectric materials when decomposed electrically generating substantially incombustible gases.

19. A method of insulating a conductor, the different parts of which when energized have different potentials causing an electrostatic field `which comprises applying a solid material to the conductor and treating the solid material with a mixture of ethyl-tetrachlorbenzene, ethylpentachlorbenzene and chlorinated diphenyl..

oxide.

20. The method of insulating a conductor, the.

ture comprising ethyl-tetrachlorbenzene, ethylpentachlorbenzene oxide.

22.' The method of insulating a cable provided with a conductor and a solid insulating mateand chlorinated diphenylrial, the different parts of the conductor when,

energized having different potentials causing an electrostatic field which comprises treating the solid insulating material with a mixture of 20% to 80% by weight of a mixture of ethyl-tetrachlorbenzene, ethyl-pentachlorbenzene and 80% to 20% by weight chlorinated diphenyloxide.

23. The method of insulating a capacitor provided with a plurality of spaced conductors which when energized have different potentials causing an electrostatic field which comprises interposing between said conductors a mixture of ethyltetrachlorbenzene, ethyl-pentachlorbe'nzene` and chlorinated diphenyloxide.

24. The method of insulating a capacitor provided with a plurality of conductors which when energized have different potentials and which are separated by a solid dielectric which comprises treating the solid dielectric with a mixture of ethyl-tetrachlorbenzene, ethyl pentachlorbenzene and chlorinated diphenyloxide.

25. The method of. insulating a plurality of conductors which when energized have different potentials causing an electrostatic field which comprises interposing between the conductors a porous paper and treating the porous paper with a mixture of 20% to 80% by weight ethyl-tetrachlorbenzene and 80% to 20% by weight chlorinated diphenyloxide.

26. The method of insulating a condenser provided with a plurality of conductors spaced apart and having interposed therebetween a solid porous dielectric, the conductors being disposed to have when energized different potentials causing an electrostatic field, treating the solid porous dielectric .with a mixture of 20% to 80% by weight ethyl-tetrachlorbenzene -and ethyl-pentachlorbenzene, the mixture consisting of 20% to 80% by `Weight of ethyl-tetrachlorbenzene and 80% to 20% by weight of ethyl-pentachlorbenzene and chlorinated diphenyloxide.

27. A dielectric liquid for electrical apparatus comprising a saturated nuclear chlorinated lower alkyl derivative of benzene, chlorinated diphenyloxide and at least one oi' the freezing point depressors of the group consisting of trichlorbenzene, aryltrichlortetralin, isopropyltrichlorbenzene and trichlortoluene.

28. 'I'he method oi insulating a conductor from a casing which comprises interposing a. dielectric material between the conductor and casing, the dielectric material comprising a saturated nuclear chlorinated lower alkyl derivative o1' benzene, chlorinated dlphenyloxide and at least one of the group of freezing point depressors, trichlorbenzene, trichlortolne, isopropyl-trichlcrbenzene and aryltrichlortetralin. g

29. A dielectric liquid for electrical apparatus comprising, in combination, a nuclear chlorinated mono-alkyl derivative of benzene containing not more than 7 carbon atoms in the saturated alkyl side-chain and chlorinated diphenyl oxide.

30. A dielectric liquid for electrical apparatus comprising, in combination, a nuclear chlorinated mono-alkyl derivative of benzene containing not more than 7 carbon atoms in a. saturated alkyl side-chain, chlorinated diphenyl oxide and at least one of the group of freezing point depressors consisting of trichlorbenzene, isopropyltrichlorbenzene, trichlortoluene and aryltrichlortetralin.

3l. The method oi insulating a. conductor from a casing which comprises interposing a dielectric material between the conductor and casing, the dielectric material comprising a, nuclear chlorinated mono-alkyl derivative oi benzene containing not more than 7 carbon atoms in the alkyl sidechain and chlorinated diphenyl oxide.

32. The method ot insulating a conductor from a casing which comprises interposing a. dielectric material comprising a nuclear chlorinated monoalkyl derivative of benzene containing not more than 7 carbon -atoms in the alkyl side-chain, chlorinated diphenyl oxide, and at least one of the group of freezing point depressors consisting of trichlorbenzene, isopropyl-trichlorbenzene, trichlortoluene and aryltrichlortetralin.

JAMES G. FORD. CHARLES l". HILL. 

